The present invention generally relates to seals for pressurized garments. More specifically, the present invention relates to cuff seals for pressurized garments that can be used in low pressure environments such as outer space.
In environments having very small or no ambient gas pressure, such as high altitude or the vacuum of space, a person's respiration and circulatory balance can be problematic. Gaseous oxygen needs to be delivered to the person's lungs at a high enough pressure to cause diffusion into the blood. It has been found that an oxygen pressure of about 80 mm Hg is minimally needed for proper breathing. An oxygen pressure of about 160 mm HG is normally experienced at sea level. A pressure of about 222 mm Hg or 4.3 psi (100% oxygen) is the current design pressure of the NASA Extravehicular Mobility Unit (EMU) spacesuit.
As ambient gas pressure rises, blood pressure similarly rises. But for proper blood circulation, tissue pressure that substantially matches the blood pressure must exist. Otherwise, the circulating blood can rush into low pressure areas and pool. If tissue pressure is not sufficiently high, the veins (and particularly the small ones) will become engorged with blood. As venous engorgement continues, pressure within the veins and capillaries continues to increase. If the pressure exceeds about 10 mm Hg, measurable amounts of excess fluid can be forced through the capillary walls and accumulate in the tissues. The accumulation of fluid can result in edema and a decrease in the circulating blood volume.
To provide adequate pressure in the tissue to prevent pooling, various suits have been employed to provide a counter pressure on the tissue. In the context of space, one such suit has been a full pressure suit that is anthropomorphically shaped, gas-tight, and pressurized with oxygen. Typically, these suits have used a rigid but flexible pressure restraining outer garment. The fully pressurized suit is different from a partial pressure suit whereby the latter is partially pressurized by gas, as well as partially pressurized by an elastic material which supplies a mechanical counter pressure directly on the skin.
But, of course, a fully pressurized suit is only as beneficial as its ability to maintain pressure within the suit. Thus, concerns have existed about punctures to such suits that might cause a sudden and large pressure loss. Other concerns have focused on leaks that may cause a slow or small pressure loss but which, over time, may result in a large pressure loss. These small or slow leaks may be due to the design constraints of the suit itself, such as where a partial pressure boot joins a fully pressurized pant leg or where a partial pressure glove joins a fully pressurized sleeve. Those areas of the suit can create design difficulties since the suit needs to maintain a pressure seal at the joinder point while still allowing, for example, a foot to flex or a hand to rotate. Additional design difficulties exist since a pressure seal needs to be maintained and, at the same time, the seal needs to provide ease of donning and doffing.
A prior a cuff seal for use around a wrist (or ankle) of a full pressure suit is shown in U.S. Pat. No. 5,335,370. A partial pressure glove (or bootie) is contemplated for use with the full pressure suit. The cuff seal includes a gas impermeable outer sheath that is actually a part of the full pressure suit together with a gas impermeable inner sheath therein. One end of the inner sheath is sealed to the end of the outer sheath where the arm or leg protrudes. The inner sheath has a gas impermeable intermediate portion that becomes sealed to the arm or leg as gas pressure is introduced between the outer and inner sheaths. However, the design is somewhat complex and cumbersome in use. An example of a cuff seal that comprises an elastic band for an anti-contamination garment is shown in U.S. Pat. No. 5,555,561.
As can be seen, there is a need for an improved counter pressure garment for low pressure environments, such as outer space. In particular, there is a need for an improved cuff seal for a counter pressure garment in the area, for example, of a wearer's ankle or wrist. Irrespective of the body area, a cuff seal is needed which can hold a counter pressure equal to the breathing pressure inside a full pressure suit. Another need is for a spacesuit cuff seal that not only provides adequate counter pressure to the tissue but is also simple in design, easy to use, and can be quickly donned and doffed.